A hallmark of systemic lupus erythematosus (SLE), and murine models of lupus, is the presence of anti-double-stranded (ds) DNA Abs. Our goals are to understand how SLE-associated autoantibodies are regulated in healthy individuals and to identify the mechanisms underlying their expression in autoimmunity. The approach we have taken is to develop a transgenic (Tg) model using a heavy chain-only Tg (VH3H9) which can pair with endogenous light chains to generate a spectrum of anti-DNA and non-DNA antibodies (Abs). The advantage of this model is that the development of anti-dsDNA B cells can be tracked in the context of a diverse B cell repertoire in non- autoimmune and autoimmune-prone backgrounds. Aim 1 of this competitive renewal is to compare the effects of distinct genetic mutations that are known to result in the production of SLE-associated autoantibodies on the phenotype and functional capacity of anti-dsDNA B cells. Specifically, lpr/lpr, gld/gld, and lyn-/- mice will be studied. Furthermore, the regulation of dsDNA B cells will also be investigated in induced models of SLE. Using the VH3H9 Tg in MRL-lpr/lpr mice, we have identified changes in the developmental status and tissue localization of anti-dsDNA B cells that precede autoantibody production. Aim II is to understand the mechanisms behind these phenomena, with particular emphasis on identifying the role that defective Fas (lpr/lpr) plays in autoantibody expression. Aim III is to characterize the nature and significance of the CD4 T cells that co-localize with anti-dsDNA B cells in MRL-lpr/lpr mice. The novel aspect of the proposed studies is that, in the context of the VH3H9 Tg, we can follow the fate of anti-dsDNA B cells under diverse circumstances to begin to identify steps that lead to autoantibody production. Knowledge of the parameters that influence the production of autoantibodies may inspire more targeted therapy for SLE.